Pressure devices keep Nestlé's heat exchangers clean

Konolfingen, Switzerland - Nestlé's Product Technology Centre (PTC) in Konolfingen  - one of 24 group research centres worldwide -  focuses mainly on developing products and production processes for milk-based infant foods, special diet nutrition and healthcare foods. The work includes researching recipes and testing processes for all operational Nestlé companies worldwide requiring new products for these areas.

The Swiss testing facility recently installed pressure transmitters equipped with hygienic stainless steel process connections for  pressure measurement at the facility’s heat exchangers. The Baumer's ED701 series devices,  which were already being used on homogenisers, mills and filling equipment at the PTC, feature aseptic (DIN 11864-1) screw connections.

Depending on the processes to be tested, up to six heat exchangers are used for heating and/or cooling the products, with the temperatures going up to 150°C. At high temperatures, the products precipitate protein, which then sediments at the heat exchanger’s metal plates. If there is too much sediment on the exchanging face, the differential pressure between the product and medium side rises and the heat exchangers have to be cleaned.

The PTC developers test recipes and manufacturing processes with different kinds of liquid products ranging from milk to dessert crème. Among other results, the tests show the possible range of process temperatures between medium and product as well as the time period the production can run without the heat exchanger needing to be cleaned.

The differential pressure is measured by the Baumer's piezo-resistive pressure transmitter, which is based on a silicon sensor designed for high precision across a wide temperature range. The sensor is anodically bonded to a stable glass base attached to a stainless steel construction,designed for thermal isolation, which a stainless steel diaphragm and special filling liquid isolate the sensor from the process medium.

The electronics are located within the hermetically sealed transmitter housing, making the ED 701 extremely resistant to humidity, shock and vibration. Depending on the choice of the electrical connection, the protection classes vary from IP 65 to IP 67. The electronics’ core piece is a micro-controller compensating any drift effects on the sensor signal due to temperature changes. Therefore, these effects can be eliminated over a wide range of temperatures with a short response time.

The ED 701 is available with a great variety of pressure and electrical connections, a 4…20 mA current loop and various voltage output signals. The product line features a short response time (max. 5 ms) and an enhanced repeatability and long-term stability.

For heat exchanger applications, the pressure transmitters were constructed with an accuracy of 0.4% FS and a compensated temperature range of -10 to 125°C (on the cooling water side) respectively a high medium temperature of 300°C maximum (on the heating side). The measuring range of the gauge pressure covers 0 to 20 bar.

As a new process connection was also required for the new milk tube, the Nestlé PTC developed a special adapter for the ED701 in co-operation with Baumer. Whereas Baumer delivered a range of hygienic, replaceable process connections made of acid-proof stainless steel for the pressure-receiving side, the matching part on the product side was constructed by Nestlé. The connections were developed according to the demands of the food industry fulfilling the FDA and EHEDG criteria.

“For the milk tube fitting, Baumer offered us the CombiConnect adapter, which we found most suitable thanks to its flush-mounted O-ring”, said Ernst Strahm, measurement technologist at the Nestlé PTC in Konolfingen. “For a hygienic pressure measurement, the quality of the measuring devices is the decisive criterion. With the ED701, we have had consistently good experiences.”